Ion channel TRPV2 is critical in enhancing B cell activation and function.

The function of transient receptor potential vanilloid (TRPV) cation channels governing B cell activation remains to be explored. We present evidence that TRPV2 is highly expressed in B cells and plays a crucial role in the formation of the B cell immunological synapse and B cell activation. Physiologically, TRPV2 expression level is positively correlated to influenza-specific antibody production and is low in newborns and seniors. Pathologically, a positive correlation is established between TRPV2 expression and the clinical manifestations of systemic lupus erythematosus (SLE) in adult and child SLE patients. Correspondingly, mice with deficient TRPV2 in B cells display impaired antibody responses following immunization. Mechanistically, the pore and N-terminal domains of TRPV2 are crucial for gating cation permeation and executing mechanosensation in B cells upon antigen stimulation. These processes synergistically contribute to membrane potential depolarization and cytoskeleton remodeling within the B cell immunological synapse, fostering efficient B cell activation. Thus, TRPV2 is critical in augmenting B cell activation and function.

Up-regulation of sortase-dependent pili in Bifidobacterium longum BBMN68 in response to bile stress enhances its adhesion to HT-29 cells.

Adhesion to gastrointestinal tract is crucial for bifidobacteria to exert their probiotic effects. Our previous work found that bile salts significantly enhance the adhesion ability of Bifidobacterium longum BBMN68 to HT-29 cells. In this study, trypsin-shaving and LC-MS/MS-based surface proteomics were employed to identify surface proteins involved in bile stress response. Among the 829 differentially expressed proteins, 56 up-regulated proteins with a fold change >1.5 were subjected to further analysis. Notably, the minor pilin subunit FimB was 4.98-fold up-regulated in response to bile stress. In silico analysis and RT-PCR confirmed that gene fimB, fimA and srtC were co-transcribed and contributed to the biosynthesis of sortase-dependent pili Pil1. Moreover, scanning electron microscopy and immunogold electron microscopy assays showed increased abundance and length of Pil1 on BBMN68 under bile stress. As the major pilin subunit FimA serves as adhesion component of Pil1, an inhibition assay using anti-FimA antibodies further confirmed the critical role of Pil1 in mediating the adhesion of BBMN68 to HT-29 cells under bile stress. Our findings suggest that the up-regulation of Pil1 in response to bile stress enhances the adhesion of BBMN68 to intestinal epithelial cells, highlighting a novel mechanism of gut persistence in B. longum strains.

Liver macrophages and sinusoidal endothelial cells execute vaccine-elicited capture of invasive bacteria.

Vaccination has substantially reduced the morbidity and mortality of bacterial diseases, but mechanisms of vaccine-elicited pathogen clearance remain largely undefined. We report that vaccine-elicited immunity against invasive bacteria mainly operates in the liver. In contrast to the current paradigm that migrating phagocytes execute vaccine-elicited immunity against blood-borne pathogens, we found that invasive bacteria are captured and killed in the liver of vaccinated host via various immune mechanisms that depend on the protective potency of the vaccine. Vaccines with relatively lower degrees of protection only activated liver-resident macrophage Kupffer cells (KCs) by inducing pathogen-binding immunoglobulin M (IgM) or low amounts of IgG. IgG-coated pathogens were directly captured by KCs via multiple IgG receptors FcγRs, whereas IgM-opsonized bacteria were indirectly bound to KCs via complement receptors of immunoglobulin superfamily (CRIg) and complement receptor 3 (CR3) after complement C3 activation at the bacterial surface. Conversely, the more potent vaccines engaged both KCs and liver sinusoidal endothelial cells by inducing higher titers of functional IgG antibodies. Endothelial cells (ECs) captured densely IgG-opsonized pathogens by the low-affinity IgG receptor FcγRIIB in a "zipper-like" manner and achieved bacterial killing predominantly in the extracellular milieu via an undefined mechanism. KC- and endothelial cell-based capture of antibody-opsonized bacteria also occurred in FcγR-humanized mice. These vaccine protection mechanisms in the liver not only provide a comprehensive explanation for vaccine-/antibody-boosted immunity against invasive bacteria but also may serve as in vivo functional readouts of vaccine efficacy.

Amino Acid Starvation-Induced Glutamine Accumulation Enhances Pneumococcal Survival.

Bacteria are known to cope with amino acid starvation by the stringent response signaling system, which is mediated by the accumulation of the (p)ppGpp alarmones when uncharged tRNAs stall at the ribosomal A site. While a number of metabolic processes have been shown to be regulatory targets of the stringent response in many bacteria, the global impact of amino acid starvation on bacterial metabolism remains obscure. This work reports the metabolomic profiling of the human pathogen Streptococcus pneumoniae under methionine starvation. Methionine limitation led to the massive overhaul of the pneumococcal metabolome. In particular, methionine-starved pneumococci showed a massive accumulation of many metabolites such as glutamine, glutamic acid, lactate, and cyclic AMP (cAMP). In the meantime, methionine-starved pneumococci showed a lower intracellular pH and prolonged survival. Isotope tracing revealed that pneumococci depend predominantly on amino acid uptake to replenish intracellular glutamine but cannot convert glutamine to methionine. Further genetic and biochemical analyses strongly suggested that glutamine is involved in the formation of a "prosurvival" metabolic state by maintaining an appropriate intracellular pH, which is accomplished by the enzymatic release of ammonia from glutamine. Methionine starvation-induced intracellular pH reduction and glutamine accumulation also occurred to various extents under the limitation of other amino acids. These findings have uncovered a new metabolic mechanism of bacterial adaptation to amino acid limitation and perhaps other stresses, which may be used as a potential therapeutic target for infection control. IMPORTANCE Bacteria are known to cope with amino acid starvation by halting growth and prolonging survival via the stringent response signaling system. Previous investigations have allowed us to understand how the stringent response regulates many aspects of macromolecule synthesis and catabolism, but how amino acid starvation promotes bacterial survival at the metabolic level remains largely unclear. This paper reports our systematic profiling of the methionine starvation-induced metabolome in S. pneumoniae. To the best of our knowledge, this represents the first reported bacterial metabolome under amino acid starvation. These data have revealed that the significant accumulation of glutamine and lactate enables S. pneumoniae to form a "prosurvival" metabolic state with a lower intracellular pH, which inhibits bacterial growth for prolonged survival. Our findings have provided insightful information on the metabolic mechanisms of pneumococcal adaptation to nutrient limitation during the colonization of the human upper airway.

Identification of the mouse Kupffer cell receptors recognizing pneumococcal capsules by affinity screening.

Kupffer cells (KCs) are the major sentinels to guard the bloodstream by recognizing diverse microbial ligands of blood-borne pathogens. Here, we establish a protocol for identifying the KC receptors recognizing the capsular polysaccharides (CPSs) of low-virulence Streptococcus pneumoniae in a mouse model. This protocol includes preparation of CPS-coated microspheres and KC membrane proteins, affinity pulldown of CPS-binding proteins, and functional validation of the CPS receptors. This protocol provides a platform to investigate the receptor-ligand interactions between KCs and encapsulated bacteria. For complete details on the use and execution of this protocol, please refer to An et al. (2022).1.

Capsule type defines the capability of Klebsiella pneumoniae in evading Kupffer cell capture in the liver.

Polysaccharide capsule is the main virulence factor of K. pneumoniae, a major pathogen of bloodstream infections in humans. While more than 80 capsular serotypes have been identified in K. pneumoniae, only several serotypes are frequently identified in invasive infections. It is documented that the capsule enhances bacterial resistance to phagocytosis, antimicrobial peptides and complement deposition under in vitro conditions. However, the precise role of the capsule in the process of K. pneumoniae bloodstream infections remains to be elucidated. Here we show that the capsule promotes K. pneumoniae survival in the bloodstream by protecting bacteria from being captured by liver resident macrophage Kupffer cells (KCs). Our real-time in vivo imaging revealed that blood-borne acapsular K. pneumoniae mutant is rapidly captured and killed by KCs in the liver sinusoids of mice, whereas, to various extents, encapsulated strains bypass the anti-bacterial machinery in a serotype-dependent manner. Using capsule switched strains, we show that certain high-virulence (HV) capsular serotypes completely block KC's capture, whereas the low-virulence (LV) counterparts confer partial protection against KC's capture. Moreover, KC's capture of the LV K. pneumoniae could be in vivo neutralized by free capsular polysaccharides of homologous but not heterologous serotypes, indicating that KCs specifically recognize the LV capsules. Finally, immunization with inactivated K. pneumoniae enables KCs to capture the HV K. pneumoniae. Together, our findings have uncovered that KCs are the major target cells of K. pneumoniae capsule to promote bacterial survival and virulence, which can be reversed by vaccination.

Functional vulnerability of liver macrophages to capsules defines virulence of blood-borne bacteria.

Many encapsulated bacteria use capsules to cause invasive diseases. However, it remains largely unknown how the capsules enhance bacterial virulence under in vivo infection conditions. Here we show that the capsules primarily target the liver to enhance bacterial survival at the onset of blood-borne infections. In a mouse sepsis model, the capsules enabled human pathogens Streptococcus pneumoniae and Escherichia coli to circumvent the recognition of liver-resident macrophage Kupffer cells (KCs) in a capsular serotype-dependent manner. In contrast to effective capture of acapsular bacteria by KCs, the encapsulated bacteria are partially (low-virulence types) or completely (high-virulence types) "untouchable" for KCs. We finally identified the asialoglycoprotein receptor (ASGR) as the first known capsule receptor on KCs to recognize the low-virulence serotype-7F and -14 pneumococcal capsules. Our data identify the molecular interplay between the capsules and KCs as a master controller of the fate and virulence of encapsulated bacteria, and suggest that the interplay is targetable for therapeutic control of septic infections.

Progress in research on natural cellulosic fibre modifications by polyelectrolytes.

In order to improve the mechanical properties and functionalities of natural cellulosic fibres, this paper first analyzed the characteristics of natural cellulosic fibres and the conventional modification methods of natural cellulosic fibres, and then focused on the polyelectrolytes modified natural cellulosic fibres. The main methods and process parameters of this modification were described in detail; the modification effects of polyelectrolytes on different types of fibres were systematically summarized; the influencing factors on modification of fibres were also discussed in depth; the characterization methods of polyelectrolytes modified fibres were analyzed in detail. Finally, the main application fields of polyelectrolytes modified fibres were systematically summarized.

Long-term corrosion protection of styrene acrylic coatings enhanced by fluorine and nitrogen co-doped graphene oxide.

Graphene materials are widely used as a physical barrier when applying anticorrosion polymer coatings due to their large surface area and layered structure. However, the electrical conductivity of intrinsic graphene can accelerate galvanic corrosion and shorten the protection period. In this work, fluorine and nitrogen co-doped graphene oxide (FNGO) was synthesized by a hydrothermal process and acted as an anticorrosion filler in waterborne styrene acrylic coatings. Styrene acrylic coatings with 0.4 wt% FNGO showed a corrosion current density that was two orders of magnitude lower than the other samples in the potential polarization test and the largest impedance modulus in the electrochemical impedance spectroscopy results. The outstanding corrosion protection was attributed to the graphene acting as a physical barrier and the synergistic effect of the doped fluorine and nitrogen. In addition to the 'labyrinth effect' of the graphene matrix, the nitrogen atoms inserted in the graphene plane and fluorine atoms grafted on the graphene simultaneously adjusted the electrical properties of graphene, prohibiting electron transport between it and the styrene acrylic resin matrix. This result indicates that doped graphene oxide has great potential to increase the corrosion resistance of waterborne coatings.

MetR is a molecular adaptor for pneumococcal carriage in the healthy upper airway.

Streptococcus pneumoniae resides in the human upper airway as a commensal but also causes pneumonia, bacteremia, meningitis, and otitis media. It remains unclear how pneumococci adapt to nutritional conditions of various host niches. We here show that MetR, a LysR family transcriptional regulator, serves as a molecular adaptor for pneumococcal fitness, particularly in the upper airway. The metR mutant of strain D39 rapidly disappeared from the nasopharynx but was marginally attenuated in the lungs and bloodstream of mice. RNA-seq and ChIP-seq analyses showed that MetR broadly regulates transcription of the genes involved in methionine synthesis and other functions under methionine starvation. Genetic and biochemical analyses confirmed that MetR is essential for the activation of methionine synthesis but not uptake. Co-infection of influenza virus partially restored the colonization defect of the metR mutant. These results strongly suggest that MetR is particularly evolved for pneumococcal carriage in the upper airway of healthy individuals where free methionine is severely limited, but it becomes dispensable where environmental methionine is relatively more abundant (e.g., inflamed upper airway and sterile sites). To the best of our knowledge, MetR represents the first known regulator particularly for pneumococcal carriage in healthy individuals.

Serotype Distribution, Antimicrobial Susceptibility, Multilocus Sequencing Type and Virulence of Invasive Streptococcus pneumoniae in China: A Six-Year Multicenter Study.

Background: Streptococcus pneumoniae is an important human pathogen that can cause severe invasive pneumococcal diseases (IPDs). The aim of this multicenter study was to investigate the serotype and sequence type (ST) distribution, antimicrobial susceptibility, and virulence of S. pneumoniae strains causing IPD in China. Methods: A total of 300 invasive S. pneumoniae isolates were included in this study. The serotype, ST, and antimicrobial susceptibility of the strains, were determined by the Quellung reaction, multi-locus sequence typing (MLST) and broth microdilution method, respectively. The virulence level of the strains in the most prevalent serotypes was evaluated by a mouse sepsis model, and the expression level of well-known virulence genes was measured by RT-PCR. Results: The most common serotypes in this study were 23F, 19A, 19F, 3, and 14. The serotype coverages of PCV7, PCV10, PCV13, and PPV23 vaccines on the strain collection were 42.3, 45.3, 73.3 and 79.3%, respectively. The most common STs were ST320, ST81, ST271, ST876, and ST3173. All strains were susceptible to ertapenem, levofloxacin, moxifloxacin, linezolid, and vancomycin, but a very high proportion (>95%) was resistant to macrolides and clindamycin. Based on the oral, meningitis and non-meningitis breakpoints, penicillin non-susceptible Streptococcus pneumoniae (PNSP) accounted for 67.7, 67.7 and 4.3% of the isolates, respectively. Serotype 3 strains were characterized by high virulence levels and low antimicrobial-resistance rates, while strains of serotypes 23F, 19F, 19A, and 14, exhibited low virulence and high resistance rates to antibiotics. Capsular polysaccharide and non-capsular virulence factors were collectively responsible for the virulence diversity of S. pneumoniae strains. Conclusion: Our study provides a comprehensive insight into the epidemiology and virulence diversity of S. pneumoniae strains causing IPD in China.

The MarR Family Regulator BmrR Is Involved in Bile Tolerance of Bifidobacterium longum BBMN68 via Controlling the Expression of an ABC Transporter.

In order to colonize the human gastrointestinal tract and exert their beneficial effects, bifidobacteria must effectively cope with toxic bile salts in the intestine; however, the molecular mechanism underlying bile tolerance is poorly understood. In this study, heterologous expression of a MarR family transcriptional regulator, BmrR, significantly reduced the ox bile resistance of Lactococcus lactis NZ9000, suggesting that BmrR might play a role in the bile stress response. In silico analysis combined with reverse transcription-PCR assays demonstrated that bmrR was cotranscribed with bmrA and bmrB, which encoded multidrug resistance (MDR) ABC transporters. Promoter prediction and electrophoretic mobility shift assays revealed that BmrR could autoregulate the bmrRAB operon by binding to the bmr box (ATTGTTG-6nt-CAACAAT) in the promoter region. Moreover, heterologous expression of bmrA and bmrB in L. lactis yielded 20.77-fold higher tolerance to 0.10% ox bile, compared to the wild-type strain. In addition, ox bile could disrupt the DNA binding activity of BmrR as a ligand. Taken together, our findings indicate that the bmrRAB operon is autoregulated by the transcriptional regulator BmrR and ox bile serves as an inducer to activate the bile efflux transporter BmrAB in response to bile stress in Bifidobacterium longum BBMN68.IMPORTANCE Bifidobacteria are natural inhabitants of the human intestinal tract. Some bifidobacterial strains are used as probiotics in fermented dairy production because of their health-promoting effects. Following consumption, bifidobacteria colonize the lower intestinal tract, where the concentrations of bile salts remain nearly 0.05% to 2.0%. Bile salts, as detergent-like antimicrobial compounds, can cause cellular membrane disruption, protein misfolding, and DNA damage. Therefore, tolerance to physiological bile stress is indeed essential for bifidobacteria to survive and to exert probiotic effects in the gastrointestinal tract. In B. longum BBMN68, the MarR-type regulator BmrR was involved in the bile stress response by autoregulating the bmrRAB operon, and ox bile as an inducer could increase the expression of the BmrAB transporter to enhance the bile tolerance of BBMN68. Our study represents a functional analysis of the bmrRAB operon in the bile stress response, which will provide new insights into bile tolerance mechanisms in Bifidobacterium and other bacteria.

Characterization of Streptococcus pluranimalium from a cattle with mastitis by whole genome sequencing and functional validation.

BACKGROUND: Streptococcus pluranimalium is a new member of the Streptococcus genus isolated from multiple different animal hosts. It has been identified as a pathogen associated with subclinical mastitis, valvular endocarditis and septicaemia in animals. Moreover, this bacterium has emerged as a new pathogen for human infective endocarditis and brain abscess. However, the patho-biological properties of S. pluranimalium remain virtually unknown. The aim of this study was to determine the complete genome sequence of S. pluranimalium strain TH11417 isolated from a cattle with mastitis, and to characterize its antimicrobial resistance, virulence, and carbon catabolism. RESULTS: The genome of S. pluranimalium TH11417, determined by single-molecule real-time (SMRT) sequencing, consists of 2,065,522 base pair (bp) with a G + C content of 38.65%, 2,007 predicted coding sequence (CDS), 58 transfer RNA (tRNA) genes and five ribosome RNA (rRNA) operons. It contains a novel ISSpl1 element (a memeber of the IS3 family) and a Ф11417.1 prophage that carries the mef(A), msr(D) and lnu(C) genes. Consistently, our antimicrobial susceptibility test confirmed that S. pluranimalium TH11417 was resistant to erythromycin and lincomycin. However, this strain did not show virulence in murine pneumonia (intranasal inoculation, 107 colony forming unit - CFU) and sepsis (intraperitoneal inoculation, 107 CFU) models. Additionally, this strain is able to grow with glucose, lactose or galactose as the sole carbon source, and possesses a lactose-specific phosphoenolpyruvate-dependent phosphotransferase system (PTS). CONCLUSIONS: We reported the first whole genome sequence of S. pluranimalium isolated from a cattle with mastitis. It harbors a prophage carrying the mef(A), msr(D) and lnu(C) genes, and is avirulent in the murine infection model.

An Interleukin-25-Mediated Autoregulatory Circuit in Keratinocytes Plays a Pivotal Role in Psoriatic Skin Inflammation.

Psoriasis is a chronic autoinflammatory skin disease. Although interleukin-17, derived from lymphocytes, has been shown to be critical in psoriasis, the initiation and maintenance of chronic skin inflammation has not been well understood. IL-25 (also called IL-17E), another IL-17 family cytokine, is well known to regulate allergic responses and type 2 immunity. Here we have shown that IL-25, also highly expressed in the lesional skin of psoriasis patients, was regulated by IL-17 in murine skin of a imiquimod (IMQ)-induced psoriasis model. IL-25 injection induced skin inflammation, whereas germline or keratinocyte-specific deletion of IL-25 caused resistance to IMQ-induced psoriasis. Via IL-17RB expression in keratinocytes, IL-25 stimulated the proliferation of keratinocytes and induced the production of inflammatory cytokines and chemokines, via activation of the STAT3 transcription factor. Thus, our data demonstrate that an IL-17-induced autoregulatory circuit in keratinocytes is mediated by IL-25 and suggest that this circuit could be targeted in the treatment of psoriasis patients.

Reduced graphene oxide doped predominantly with CF2 groups as a superior anode material for long-life lithium-ion batteries.

A fluorine-doped reduced graphene oxide (F-rGO), predominantly in the form of CF2 groups, was synthesized using the reduced-graphene-oxide precursor devoid of residual hydroxyl and carboxyl groups through a solvothermal process. The vacancies and defects accompanying the formation of the highly stable and electrochemically inert CF2 groups contribute to the excellent cycling stability of F-rGO, when it is applied as the anode material in a lithium-ion battery.

Solid-State Fluorescence of Fluorine-Modified Carbon Nanodots Aggregates Triggered by Poly(ethylene glycol).

Solid-state fluorescent carbon quantum dots (QDs) can be used for the encryption of security information. Controlling the dispersion and aggregation of the QDs is crucial for switching their solid-state fluorescence "on" and "off." The use of polymers has been proposed to slightly separate the QDs inside aggregates to trigger their fluorescence. However, the complex interactions between the QDs and flexible polymer chains make this process challenging. Here, fluorine-modified carbon nanodots (FCDs) were used in a solution as the printing ink. After printing, the FCDs were aggregated on paper via hydrogen bonds, thereby quenching the fluorescence. After a poly(ethylene glycol) (PEG) treatment, the FCDs exhibited yellow solid-state fluorescence due to an increased interdot spacing. The fluorescence intensity and emission wavelength could be tuned by varying the molecular weight and quantity of PEG used. Finally, we demonstrated a high-resolution encryption and decryption system based on the PEG-triggered fluorescence of FCDs.

Tetracarboxylated Azobenzene/Polymer Supramolecular Assemblies as High-Performance Multiresponsive Actuators.

Multistimuli-responsive polymers are materials of emerging interest but synthetically challenging. In this work, supramolecular assembly was employed as a facile and effective approach for constructing 3,3',5,5'-azobenzenetetracarboxylic acid (H4abtc)/poly(diallyldimethylammonium chloride) (PDAC) supramolecules. Structural transformations of H4abtc can be induced by light, mechanical force, and heat and influenced by free volume. Thus, the fabricated free-standing H4abtc/PDAC film underwent bending/unbending movements upon treatment with light, humidity, or temperature, as asymmetric structural transformations on either side of the film generated asymmetric contraction/stretching forces. Fast rates of shape recovery were achieved for the film on exposure to gently flowing humid nitrogen. The bending/unbending motions are controllable, reversible, and repeatable. Hence, this light-, humido-, and thermo-responsive film has great potential in device applications for advanced functions.

New Insights into the Formation of Viable but Nonculturable Escherichia coli O157:H7 Induced by High-Pressure CO2.

UNLABELLED: The formation of viable but nonculturable (VBNC) Escherichia coli O157:H7 induced by high-pressure CO2 (HPCD) was investigated using RNA sequencing (RNA-Seq) transcriptomics and isobaric tag for relative and absolute quantitation (iTRAQ) proteomic methods. The analyses revealed that 97 genes and 56 proteins were significantly changed upon VBNC state entry. Genes and proteins related to membrane transport, central metabolisms, DNA replication, and cell division were mainly downregulated in the VBNC cells. This caused low metabolic activity concurrently with a division arrest in cells, which may be related to VBNC state formation. Cell division repression and outer membrane overexpression were confirmed to be involved in VBNC state formation by homologous expression of z2046 coding for transcriptional repressor and ompF encoding outer membrane protein F. Upon VBNC state entry, pyruvate catabolism in the cells shifted from the tricarboxylic acid (TCA) cycle toward the fermentative route; this led to a low level of ATP. Combating the low energy supply, ATP production in the VBNC cells was compensated by the degradation of l-serine and l-threonine, the increased AMP generation, and the enhanced electron transfer. Furthermore, tolerance of the cells with respect to HPCD-induced acid, oxidation, and high CO2 stresses was enhanced by promoting the production of ammonia and NADPH and by reducing CO2 production during VBNC state formation. Most genes and proteins related to pathogenicity were downregulated in the VBNC cells. This would decrease the cell pathogenicity, which was confirmed by adhesion assays. In conclusion, the decreased metabolic activity, repressed cell division, and enhanced survival ability in E. coli O157:H7 might cause HPCD-induced VBNC state formation. IMPORTANCE: Escherichia coli O157:H7 has been implicated in large foodborne outbreaks worldwide. It has been reported that the presence of as few as 10 cells in food could cause illness. However, the presence of only 0.73 to 1.5 culturable E. coli O157:H7 cells in salted salmon roe caused infection in Japan. Investigators found that E. coli O157:H7 in the viable but nonculturable (VBNC) state was the source of the outbreak. So far, formation mechanisms of VBNC state are not well known. In a previous study, we demonstrated that high-pressure CO2 (HPCD) could induce the transition of E. coli O157:H7 into the VBNC state. In this study, we used RNA-Seq transcriptomic analysis combined with the iTRAQ proteomic method to investigate the formation of VBNC E. coli O157:H7 induced by HPCD treatment. Finally, we proposed a putative formation mechanism of the VBNC cells induced by HPCD, which may provide a theoretical foundation for controlling the VBNC state entry induced by HPCD treatment.

Epigenetic Switch Driven by DNA Inversions Dictates Phase Variation in Streptococcus pneumoniae.

DNA methylation is an important epigenetic mechanism for phenotypic diversification in all forms of life. We previously described remarkable cell-to-cell heterogeneity in epigenetic pattern within a clonal population of Streptococcus pneumoniae, a leading human pathogen. We here report that the epigenetic diversity is caused by extensive DNA inversions among hsdSA, hsdSB, and hsdSC, three methyltransferase hsdS genes in the Spn556II type-I restriction modification (R-M) locus. Because hsdSA encodes the sequence recognition subunit of this type-I R-M DNA methyltransferase, these site-specific recombinations generate pneumococcal cells with variable HsdSA alleles and thereby diverse genome methylation patterns. Most importantly, the DNA methylation pattern specified by the HsdSA1 allele leads to the formation of opaque colonies, whereas the pneumococci lacking HsdSA1 produce transparent colonies. Furthermore, this HsdSA1-dependent phase variation requires intact DNA methylase activity encoded by hsdM in the Spn556II (renamed colony opacity determinant or cod) locus. Thus, the DNA inversion-driven ON/OFF switch of the hsdSA1 allele in the cod locus and resulting epigenetic switch dictate the phase variation between the opaque and transparent phenotypes. Phase variation has been well documented for its importance in pneumococcal carriage and invasive infection, but its molecular basis remains unclear. Our work has discovered a novel epigenetic cause for this significant pathobiology phenomenon in S. pneumoniae. Lastly, our findings broadly represents a significant advancement in our understanding of bacterial R-M systems and their potential in shaping epigenetic and phenotypic diversity of the prokaryotic organisms because similar site-specific recombination systems widely exist in many archaeal and bacterial species.

Complete genome sequence of Lactobacillus helveticus CAUH18, a potential probiotic strain originated from koumiss.

Here we report the complete genome sequence of Lactobacillus helveticus CAUH18, a new strain isolated from traditional fermented dairy product koumiss. Its genome has a circular 2.16Mb chromosome with no plasmid. The genome sequence indicated that this strain harbors a gene cluster involved in a novel exopolysaccharides (EPS) biosynthesis and a gene encoding cell-surface aggregation-promoting factors (APFs) to facilitate its colonization in gastrointestinal tract (GIT). This genome sequence provides a basis for further studies about its molecular genetics and probiotic functions.